Methods and apparatus to generate signatures representative of media

ABSTRACT

Methods and apparatus to generate signatures representative of media are disclosed. An example method includes transforming a block of samples from a time-domain representation to a frequency-domain representation comprising multiple frequency bands, determining a signature function by fitting a curve to at least a subset of the frequency bands, and calculating signature values for the block. Calculating the tuple includes calculating a first angle between a reference line and a first line that is tangent to the signature function at a first index, calculating a second angle between the reference line and a second line that is tangent to the signature function at a second index, calculating a third angle between the reference line and a third line that is tangent to the signature function at a third index, and creating the signature values based on the first angle, the second angle, and the third angle.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to media monitoring, multimediacontent search and retrieval and, more particularly, to methods andapparatus to generate signatures representative of media.

BACKGROUND

Signature generation and matching techniques are often used intelevision and radio audience metering applications. Signatures are alsoequivalently known, and frequently referred to, as fingerprints, and areimplemented using several methods for generating and matchingsignatures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example media identification system to generatesignatures of signals in accordance with the teachings of thisdisclosure.

FIG. 2 is a block diagram of an example signature generator that may beused to implement the signature generator and/or the reference signaturegenerator of FIG. 1.

FIG. 3 is a block diagram of an example signature comparator that may beused to implement the example signature analyzer of FIG. 1.

FIG. 4 shows an example audio signal including a set of samplesrepresentative of the audio signal.

FIG. 5 shows an example frequency-domain representation of the exampleaudio signal represented by the samples of FIG. 4.

FIG. 6 shows an example signature function generated by the examplecurve fitter of FIG. 2.

FIG. 7 shows example signature functions resulting from blocks of signalsamples representative of a same block of audio.

FIG. 8A shows example angles calculated for a set of signatures forcorresponding blocks of audio samples from a first audio item.

FIG. 8B shows example angles calculated for a set of signatures forcorresponding blocks of audio samples from a second audio item differentthan the first audio item of FIG. 8A.

FIG. 9 shows an example query signature and an example referencesignature assigned to respective indices for comparison.

FIG. 10 shows example correlation coefficients calculated for theexample query signature and the example reference signature of FIG. 9.

FIG. 11 is a flowchart representative of example computer readableinstructions that may be executed to implement the example signaturegenerators and/or the example reference signature generator of FIGS. 1and/or 2 to generate an audio signature.

FIG. 12 is a flowchart representative of example computer readableinstructions that may be executed to implement the example transformerof FIG. 2 to transform a block of audio into a frequency-domainrepresentation.

FIG. 13 is a flowchart representative of example computer readableinstructions that may be executed to implement the example tuplegenerator of FIG. 2 to generate a tuple for a block of audio.

FIGS. 14A, 14B, and 14C collectively show a flowchart representative ofexample computer readable instructions that may be executed to implementthe example signature analyzer of FIG. 1 and/or the example signaturecomparator of FIG. 3 to match an audio signature to a referencesignature.

FIG. 15 is a block diagram of an example processor platform capable ofexecuting the instructions of FIGS. 11, 12, 13, and/or 14A-14C toimplement the apparatus of FIGS. 1, 2, and/or 3.

The figures are not to scale. Wherever appropriate, the same referencenumbers will be used throughout the drawing(s) and accompanying writtendescription to refer to the same or like parts.

DETAILED DESCRIPTION

Fingerprint or signature-based media monitoring techniques generally useone or more inherent characteristics of the monitored media during amonitoring time interval to generate a substantially unique proxy forthe media. Such a proxy is referred to as a signature or fingerprint,and can take any form (e.g., a series of digital values, a waveform,etc.) representative of any aspect(s) of the media signal(s)(e.g., theaudio and/or video signals forming the media presentation beingmonitored). Good signatures are 1) repeatable when processing the samemedia presentation even when the media is subjected to differenteffects, and 2) are unique relative to presentations of different media.Accordingly, the terms “fingerprint,” “digital fingerprint,” “digitalsignature,” and “signature” are used interchangeably herein.

Prior techniques for signature-based media monitoring involvedetermining (e.g., generating and/or collecting) signature(s)representative of a media signal (e.g., an audio signal and/or a videosignal) output by a monitored media device and comparing the querysignature(s) to one or more reference signatures corresponding to known(e.g., reference) media sources. As used herein, the term “query audio”or “query signal” refer to audio or other signals, respectively, fromwhich a signature is generated at a monitoring site to attempt toidentify the query audio or query signal. Similarly, as used herein, theterm “query signature” refers to a signature that has been collectedfrom a monitoring site and is to be compared to one or more referencesignatures to attempt to identify a match. Various comparison criteria,such as a cross-correlation value, a Hamming distance, etc., can beevaluated to determine whether a query signature matches a particularreference signature. When a match between the query signature and one ofthe reference signatures is found, the monitored media can be identifiedas corresponding to the particular reference media represented by thereference signature that matched the query signature.

Because attributes, such as an identifier of the media, a presentationtime, a broadcast channel, etc., are collected for the referencesignature, these attributes may then be associated with the monitoredmedia whose query signature matched the reference signature. An exampleof a prior system for identifying media based on codes and/or signaturesis disclosed in Thomas, U.S. Pat. No. 5,481,294.

Example methods and apparatus disclosed herein generate signatures, orfingerprints, that uniquely represent signals such as audio, video,still images, and/or other types of signals. Relative to priortechniques to generate signatures that have been proposed, examplemethods and apparatus disclosed herein provide computationally efficientmethods of generating signatures that provide additional efficienciesthrough high data compression of a signal into a signature.Additionally, example methods and apparatus disclosed herein are robustto distortions introduced by noise, signal distortion (e.g., increasedand/or decreased volume, bass and/or treble frequencies for audiosignals) and/or caused by different data capture methods (e.g.,free-field audio capture via microphone, wired transmission via line-in,and/or digital transmission). As a result, example methods and apparatusdisclosed herein enable an energy-efficient method for generatingsignatures that can be performed, for example, by mobile devices forwhich prior techniques were too computationally-intensive and/orenergy-intensive to be tolerated by most users of such devices.

Examples disclosed herein obtain (e.g., capture) an audio signal andsample the audio signal to create a block of samples (e.g., 576 samplesrepresenting 0.072 seconds of audio, etc.). Disclosed examples transformthe block of samples from a time-domain representation to afrequency-domain representation by, for example, applying a polyphasequadrature filter (PQF) to the block of samples. Disclosed examplesapply energy compaction to the example frequency-domain representationusing, for example, a modified discrete cosine transform (MDCT). Theresult of the energy compaction is a set of frequency bands havingrespective energies.

Examples disclosed herein perform curve fitting on the energy-compactedfrequency bands to obtain a signature function representative of theaudio block. In some examples, the signature function is a quadraticfunction (e.g., a second-order function) that is fit to the frequencybands using least squares error (LSE) analysis. In some examples, areduced set of the frequency bands are selected for generating thesignature function.

Examples disclosed herein compress the signature function into a set ofrepresentative values by calculating a set of angles. In some disclosedexamples, each of the angles is determined to be between a line tangentto the signature function and a reference line (e.g., the horizontalaxis of a graph corresponding to the signature function or,equivalently, a line parallel to the horizontal axis). In some examples,an initial angle is calculated between the reference line and a firstline that is tangent to a signature function at a first point on thesignature function. The first tangent line is used to calculate a secondpoint on the signature function at which a second tangent line isdetermined. A second angle is calculated based on the second tangentline and the reference line. The second tangent line is used tocalculate a third point on the signature function at which a thirdtangent line is determined. A third angle is calculated based on thethird tangent line and the reference line. Example methods and apparatusdisclosed herein generate signature values, such as a tuple, includingthe first, second, and third angles to represent the signature functionand, thus, the block of audio. In other examples, more or fewer anglesmay be used to represent the block of audio. As used herein, a tuplerefers to an ordered set of values. An n-tuple refers to a tuple havingn ordered values. For example, a 3-tuple would include 3 values (e.g.,S₀, S₁, S₂) in an order <S₀, S₁, S₂> that is different than a 3-tupleconsisting of <S₁, S₂, S₀>.

Examples disclosed herein generate a signature (or fingerprint) for anitem of audio (e.g., a song, an audio clip, etc.), including sequentialblocks of audio, as an ordered set of tuples representative of theblocks, where each tuple represents a block of audio. Thus, a signaturemay include any number of tuples to represent a corresponding number ofblocks of audio. Signatures are not necessarily limited to particularlengths or numbers of tuples.

Examples disclosed herein identify matches and/or partial matchesbetween an item of audio (e.g., query audio) and reference audio (e.g.,a library of reference audio segments) by comparing the signatures ofthe query audio and the reference audio. In some examples, a query audiosignature is compared to a reference audio signature by determiningcorrelations between the tuples of the respective signatures. In someexamples, Pearson product-moment correlations are calculated on asliding window of the tuples to obtain a set of correlation values.Additionally or alternatively, the tuples (e.g., angles) may be arrangedand/or modified to support a Hamming distance comparison and/or anyother matching process to compare signatures.

In some examples, a match between the portion of the query audio and theportion of the reference audio is identified when at least a thresholdportion of the set of correlation values resulting from comparing thesignatures of the query audio and the reference audio satisfies acorrelation threshold. In some examples, a match between the query audioitem and the reference audio item is identified when at least athreshold number or percentage of matches are identified between thecompared portions of the query audio item and the portions of thereference audio item.

FIG. 1 illustrates an example media identification system 100 togenerate digital signatures of signals. The example media identificationsystem 100 may be implemented as a television broadcast informationidentification system, a radio broadcast information identificationsystem, and/or an Internet media identification system (e.g., streamingmedia and/or downloaded media played on a local device), respectively.The example media identification system 100 includes a monitoring site102 (e.g., a monitored household), a reference site 104, and a centraldata collection facility 106.

Monitoring media, such as television and/or radio broadcast information,involves generating query signatures at the monitoring site 102 based onthe media. For example, the monitoring site may monitor audio data oftelevision broadcast information. The example monitoring site 102 ofFIG. 1 communicates the query signatures to the central data collectionfacility 106 via a network 108. The monitoring site 102 may be, forexample, a household for which the media consumption of an audience ismonitored. The example monitoring site 102 of FIG. 1 includes a mediadelivery device 110, a media presentation device 112, and a signaturegenerator 114. The example signature generator 114 of FIG. 1 generatesquery signatures associated with media presented at the monitoring site102.

The example reference site 104 of FIG. 1 generates reference signaturesand communicates the reference signatures to the central data collectionfacility 106 via the network 108. The example reference site 104 isdiscussed in more detail below.

The example central data collection facility 106 of FIG. 1 identifiesthe media content represented by a query signature that is generated atthe monitoring site 102 by comparing the query signature to one or morereference signatures until a match is found. Additionally oralternatively, the example monitoring site 102 may communicate querysignatures to the reference site 104, which compares the querysignatures to one or more reference signatures. In some other examples,the example reference site 104 communicates the reference signatures tothe monitoring site 102, which compares the query signatures with thereference signatures. In some examples, the central data collectionfacility 106 is an audience measurement entity, such as The NielsenCompany.

The example media delivery device 110 of FIG. 1 may include, forexample, a set top box tuner (e.g., a cable tuner, a satellite tuner,etc.), a personal video recorder (PVR) device, a digital versatile disc(DVD) player, a compact disc (CD) player, a radio, a home theater PC(HTPC), a video game console, etc. In some examples, the media deliverydevice 110 is communicatively coupled to one or more broadcastinformation reception devices 116, such as a cable modem, a satellitedish, an antenna, and/or any other suitable device for receivingbroadcast information. The example media delivery device 110 of FIG. 1is configured to reproduce media information (e.g., audio information,video information, web pages, still images, etc.) based on, for example,broadcast information (e.g., from the broadcast information receptiondevices 116) and/or stored information (e.g., from any informationstorage medium (e.g., a DVD, a CD, a tape, etc.)). The media deliverydevice 110 is communicatively coupled to the media presentation device112 for presentation of the broadcast information and/or the storedinformation. The media presentation device 112 of FIG. 1 may be atelevision having a display device and/or a set of speakers by whichaudience members consume, for example, broadcast television information,music, movies, streaming media, etc.

The signature generator 114 of FIG. 1 generates monitored digitalsignatures based on audio information, as described in greater detailbelow. In particular, at the monitoring site 102, the signaturegenerator 114 generates query signatures based on monitored audiostreams that are reproduced by the media delivery device 110 and/orpresented by the media presentation device 112. In some examples, thesignature generator 114 is communicatively coupled to the media deliverydevice 110 and/or the media presentation device 112 via a wiredconnection such as an audio monitoring interface 118. In this manner,the signature generator 114 may obtain audio streams (e.g., digitaland/or analog signals) associated with media information (e.g., audioand/or video) that is reproduced by the media delivery device 110 and/orpresented by the media presentation device 112. Additionally oralternatively, the signature generator 114 may be communicativelycoupled to microphones (not shown) that are placed proximate to themedia presentation devices 112 to detect audio streams. The signaturegenerator 114 may also be communicatively coupled to the central datacollection facility 106 via the network 108.

The example monitoring site 102, the example reference site 104, and/orthe example central data collection facility 106 communicate information(e.g., signatures, control information, and/or configurationinformation) via the network 108. Any wired or wireless communicationsystem such as, for example, a broadband cable network, a DSL network, acellular telephone network, a satellite network, and/or any othercommunication network may be used to implement the network 108.

As shown in FIG. 1, the reference site 104 includes one or morebroadcast information tuners 120, a reference signature generator 122, atransmitter 124, a database or memory 126, and broadcast informationreception devices 128. The example reference signature generator 122 andthe transmitter 124 of FIG. 1 are communicatively coupled to the memory126 to store reference signatures in the memory 126 and/or to retrievestored reference signatures from the memory 126.

The example broadcast information tuners 120 of FIG. 1 arecommunicatively coupled to the broadcast information reception devices128, which may include a cable, an antenna, a satellite dish, and/or anyother suitable device for receiving broadcast information. Each of theexample broadcast information tuners 120 in the example of FIG. 1 isconfigured to tune to a particular broadcast channel. In the examplesystem 100 of FIG. 1, the number of broadcast information tuners 120 atthe reference site 104 is equal to the number of channels available in aparticular broadcast region. In this manner, reference signatures may begenerated for all of the media information transmitted over alltransmission means and/or all of the channels in a broadcast region.

In the example of FIG. 1, the broadcast information tuners 120communicate the audio portions of the tuned media information to thereference signature generator 122. The example reference signaturegenerator 122 obtains the audio portion of all of the media informationthat is available in a particular broadcast region. The referencesignature generator 122 generates reference signatures (using, forexample, the processing described in greater detail below) based on theaudio information and stores the generated reference signatures in thememory 126. For example, each of the plurality of signature generatorsmay be communicatively coupled to a respective one of the broadcastinformation tuners 120.

The example transmitter 124 is in communication with the memory 126. Theexample transmitter 124 retrieves reference signatures from the memory126 and communicates the retrieved reference signatures to the centraldata collection facility 106 via the network 108.

In some examples, the reference site 104 may be used as an audio streamidentification system. For example, the reference site 104 may monitorand identify audio streams associated with television broadcastinformation, radio broadcast information, Internet media information,and/or any other media. In some examples, the reference site 104monitors the content that is broadcast by broadcast stations (e.g.,television, radio, etc.) in a particular broadcast region. For example,the reference site 104 may be used to monitor music, songs, etc. thatare broadcast within a broadcast region and the number of times thatthey are broadcast. This type of media tracking may be used to determineroyalty payments, proper use of copyrights, etc. associated with eachaudio composition.

In some such examples, the reference site 104 receives all televisionand/or radio broadcast information that is available in a particularbroadcast region and generates query signatures based on the televisionand/or radio broadcast information. In some examples, the reference site104 also includes a networked monitor 121 that receives streaming media(e.g., via the Internet) for media that is delivered in a live format.In some examples, the networked monitor 121 accesses media on theInternet (e.g., in a systematic manner using a web crawler) to accessInternet-based media and to generate reference signatures based on theInternet-based media. The example broadcast information receptiondevices 128 receive television and/or radio broadcast information andthe broadcast information tuners 120 tune to the television and/or radiobroadcast stations. The number of broadcast information tuners 120 atthe reference site 104 may be equal to the number of television and/orradio broadcasting stations in a particular broadcast region. Theexample reference site 104 may include one more of the example networkedmonitors 121 to increase the speed with which reference signatures arecollected from Internet-based media.

The reference signature generator 122 receives the audio from each ofthe broadcast information tuners 120 and generate query signaturesrepresenting the audio. Although one reference signature generator 122is shown, the reference site 104 may include multiple signaturegenerators 122, each of which receives audio from one of a correspondingnumber of broadcast information tuners 120. The example referencesignature generator 122 of FIG. 1 stores the query signatures in thememory 126. The example transmitter 124 retrieves the query signaturesfrom the memory 126 and communicates the signatures to the central datacollection facility 106 via the network 108.

In the example of FIG. 1, the central data collection facility 106compares query signatures received from the monitoring site 102 toreference signatures received from the reference site 104. In addition,the example central data collection facility 106 identifies monitoredaudio streams by matching query signatures to reference signatures andusing the information corresponding to reference signatures to retrievetelevision program identification information (e.g., program title,broadcast time, broadcast channel, etc.) from a database. The examplecentral data collection facility 106 of FIG. 1 includes a receiver 130,a signature analyzer 132, a memory 134, and a signature generator 136.

The example receiver 130 of FIG. 1 receives query signatures andreference signatures via the network 108. The receiver 130 stores thequery signatures and the reference signatures in the memory 134.

The example signature analyzer 132 of FIG. 1 compares referencesignatures to query signatures. For example, the signature analyzer 132retrieves query signatures and/or reference signatures from the memory134. In some examples, the signature analyzer 132 retrieves referencesignatures and query signatures from the memory 134 and compare thequery signatures to the reference signatures until a match is found.When a reference signature is found that matches a query signature, theexample signature analyzer 132 retrieves identification information(e.g., a song title, a song track, an artist, etc.) from a databasestored in the memory 134 using the match information and/or the matchingreference signature. The example memory 134 may be implemented using anytangible computer readable storage medium such as, for example, one ormore hard drives, one or more optical storage devices, etc.

Although the signature analyzer 132 is located at the central datacollection facility 106 in the example of FIG. 1, in some other examplesthe signature analyzer 132 is located at the reference site 104. In somesuch examples, the query signatures may be communicated from themonitoring site 102 to the reference site 104 via the network 108.Alternatively, the memory 134 may be located at the monitoring site 102and reference signatures may be added periodically to the memory 134 viathe network 108 by transmitter 124. Although the signature analyzer 132is shown as a separate device from the signature generators 114 and 122in FIG. 1, the signature analyzer 132 may be combined with the referencesignature generator 122 and/or the signature generator 114. Stillfurther, although FIG. 1 depicts a single monitoring site (i.e., themonitoring site 102) and a single reference site (i.e., the referencesite 104), multiple such sites may be coupled via the network 108 to thecentral data collection facility 106.

The example signature generator 136 of FIG. 1 generates referencesignatures based on reference audio streams. The reference audio streamsmay be stored on any type of tangible computer readable storage mediumsuch as, for example, a CD, a DVD, a digital audio tape (DAT), etc.Audio owners, such as artists and/or record producing companies, maysend their audio works (i.e., music, songs, etc.) to the example centraldata collection facility 106 of FIG. 1 to be added to a referencelibrary (e.g., in the memory 134). The example signature generator 136reads the audio data from the memory 134 and generates referencesignatures based on each item of audio (e.g., each song, each X minutesof audio, etc.). The signature generator 136 stores the referencesignatures in the memory 134 for subsequent retrieval by the signatureanalyzer 132. The example memory 134 also stores identificationinformation (e.g., song title, artist name, track number, etc.)associated with each reference audio stream. In some examples, theidentification information is indexed in the memory 134 based on thereference signatures. In this manner, the central data collectionfacility 106 includes a database of reference signatures andidentification information corresponding to all known and availableaudio information.

In some examples, the monitored site 102 and/or the reference site 104return audio to the central data collection facility 106. In some suchexamples, the signature generator 136 generates signatures of the audioprovided by the monitored site 102 and/or the reference site 104.

FIG. 2 is a block diagram of an example signature generator 200 that maybe used to implement the signature generator 114, the referencesignature generator 122, and/or the signature generator 136 of FIG. 1.The example signature generator 200 of FIG. 2 includes a transducer 202,a sampler 204, a transformer 206, a curve fitter 208, a tuple generator210, and a signature generator 212. The example transformer 206 of FIG.2 includes a polyphase quadrature filter 214 and an energy compactor216. The example tuple generator 210 of FIG. 2 includes an indexselector 218 and an angle calculator 220. The example signaturegenerator 200 of FIG. 2 is described below with reference to an audiosignal. However, the example signature generator 200 of FIG. 2 may beadapted to generate signatures for any type(s) of signals, such as videosignals and/or images.

The example transducer 202 of FIG. 2 converts a physical signal into anelectrical signal. For example, in the case of audio, the exampletransducer 202 may be a microphone that converts ambient audio into ananalog or digital electrical signal representative of the ambient audio.In some examples, the transducer 202 may be omitted and/or bypassed whenconversion of a physical signal is not necessary (e.g., when anelectrical signal is received).

The example sampler 204 of FIG. 2 samples the electrical signal togenerate a set of samples (e.g., digital samples, quantitiesrepresentative of values of the sampled signal at the respective timesthe samples are taken). An example sampler 204 may be ananalog-to-digital converter (ADC) or digitizer. For example, the sampler204 may measure an electrical signal obtained from the transducer 202 togenerate a number of samples representative of a desired time periodbased on a sampling frequency. In some examples, the transducer 202 andthe sampler 204 may be omitted and/or bypassed when sampling is notnecessary (e.g., when a digital file is received).

The output from the sampler 204 (and/or a digital file containing a setof samples) is a time-domain representation of the media. The exampletransformer 206 of FIG. 2 transforms the time-domain representation ofthe media into a frequency-domain representation that includes multiplefrequency bands. Thus, the energy in the media signal is represented asthe energies of respective frequencies in the frequency-domainrepresentation. The example transformer 206 of FIG. 2 uses a polyphasequadrature filter 214 to transform the time-domain representation of themedia signal to a frequency-domain representation. In some otherexamples, the PQF 214 may be replaced with other transform techniques.

In the example of FIG. 2, the transformer 206 further applies energycompaction techniques to the frequency-domain representation (generatedby the PQF 214) using the energy compactor 216. The example energycompactor 216 of FIG. 2 uses a modified discrete cosine transform (MDCT)to concentrate the energy of the frequency-domain representation in alower number of coefficients than in the frequency-domain representationoutput by the PQF 214. In other examples, the energy compactor 216 usesother energy compaction techniques (e.g., discrete cosine transform typeIV (DCT-IV), etc.). The output of the energy compactor 216 and/or of thetransformer 206 is an energy compacted frequency-domain representationof the block of samples.

The example transformer 206 of FIG. 2 outputs the energy-compactedfrequency-domain representation to the curve fitter 208. The examplecurve fitter 208 of FIG. 2 fits a curve (e.g., a signature function) tothe energy-compacted frequency-domain representation of the mediasignal. In the illustrated example, the curve fitter 208 generates thesignature function as a quadratic function (e.g., a second-degreepolynomial function). However, polynomials of other degrees may be used.Using an example notation of the signature function f(x)=ax²+bx+c, theexample curve fitter 208 of FIG. 2 determines the coefficients a, b, andc of the signature function.

In some examples, the curve fitter 208 uses, for example, the leastsquares error technique to determine the coefficients (a, b, c) of thesignature function f(x). In the least squares error technique, the curvefitter 208 attempts to define the signature function f(x) such that thetotal of the squared errors between the signature function f(x) and theenergies of the frequency bands in the energy-compacted frequency-domainrepresentation are substantially minimized. In the example of FIG. 2,the curve fitter 208 defines the signature function f(x) over a set ofsamples, such as the number of samples in the time-domain representationof the audio block.

In the example of FIG. 2, the curve fitter 208 also calculates aderivative function f′(x) of the signature function f(x). In the exampleof FIG. 2, the derivative function f′(x) is a linear function (e.g.,f′(x)=2ax+b), because the signature function f(x) is a quadraticfunction. As described below, the example tuple generator 210 of FIG. 2uses the signature function f(x) and the derivative function f′(x) tocalculate a tuple to represent the audio block including the block ofsamples.

The example tuple generator 210 of FIG. 2 generates a tuple (e.g., a3-tuple [q, r, s]) that represents the signature function f(x) generatedby the curve fitter 208 for the audio block. The example tuple generator210 uses a set of index numbers (e.g., whole numbers) as input values tothe signature function (e.g., index x for a signature functionf(x)=ax²+bx+c).

The example tuple generator 210 of FIG. 2 includes the index selector218 to select and/or calculate index values (x_(n)) to serve as thepoints on the signature function f(x_(n)) at which the tuple values (q,r, s) are to be calculated.

The example index selector 218 selects an initial index (x₀) (e.g.,x₀=1) in a deterministic manner. In the example of FIG. 2, the initialindex (x₀) is a standardized or predetermined value, such as x₀=1, thatis selected for the generation of every tuple in a signature. In someother examples, the index selector 218 calculates the initial index (x₀)using a formula that is based on one or more aspects of the signaturefunction f(x). For example, the index selector 218 may select theinitial index (x₀) to be a closest index value (x_(n)) to a maximumvalue of the signature function f(x) within the range in which the curvefitter 208 has defined the signature function f(x).

The example angle calculator 220 of FIG. 2 calculates values that makeup the tuple values (q, r, s). In the example of FIG. 2, the exampleangle calculator 220 calculates each tuple value (q, r, s) as an angle(e.g., in degrees) between a reference line and a line tangent to thesignature function at an index value selected by the index selector 218.In the illustrated example, the reference line is the horizontal axis(e.g., an x-axis) of a graph of the signature function f(x) or,equivalently, a line parallel to the horizontal axis of the graph.

As part of calculating the angles, the example angle calculator 220 alsocalculates the tangent lines, which are also used by the index selector218 in the example of FIG. 2 to calculate and select index values(x_(n)) subsequent to the initial index value (x₀). The example indexselector 218 and the example angle calculator 220 of FIG. 2 maydetermine any number of angles by iterating the following sequence: 1)select/calculate an index, which may be based on a prior tangent line;2) calculate the line tangent to the signature function at theselected/calculated index; and 3) calculate an angle (e.g., in degrees)between the tangent line and a reference line.

To calculate a first tangent line (e.g., for calculating the first tuplevalue and/or the first angle), the example angle calculator 220calculates a value y₀ of the signature function f(x) at the initialindex (x₀) (e.g., y₀=f(x₀)). The example angle calculator 220 alsocalculates a value of the derivative function f′(x) (i.e., the slope ofthe line tangent to the signature function f(x)) at the initial index(x₀) (e.g., y′₀=f′(x₀)). The first tangent line is a line that has avalue equal to the value of the signature function f(x) at the firstindex (e.g., y₀=f(x₀)) and that has a slope equal to the derivativefunction f′(x) at the first index e.g., y′₀=f′(x₀)).

The example index selector 218 calculates a second index value (x₁) asthe index value (x_(n)) at which the first tangent line is equal tozero. For example, the index selector 218 calculates the second indexvalue (x₁) as x₁=x₀−(y₀/y′₀)=x₀−(f(x₀)/f′(x₀)). In the example of FIG.2, the index selector 218 rounds the calculated second index to anearest whole number.

The example angle calculator 220 calculates a second tangent line (e.g.,for calculating the second tuple value and/or the second angle) bycalculating a value y₁ of the signature function f(x) at the secondindex (x₁) (e.g., y₁=f(x₁)). The example angle calculator 220 alsocalculates a value of the derivative function f′(x) (i.e., the slope ofthe line tangent to the signature function f(x)) at the second index(x₁) (e.g., y′₁=f′(x₁)). The second tangent line is a line that has avalue equal to the value of the signature function f(x) at the secondindex (e.g., y₁=f(x₁)) and that has a slope equal to the derivativefunction f′(x) at the second index e.g., y′₁=f(x₁)).

In the example of FIG. 2, the example index selector 218 calculates athird index value (x₂) as the index value (x_(n)) at which the secondtangent line is equal to zero. For example, the index selector 218calculates the third index value (x₂) asx₂=x₁−(y₁/y′₁)=x₁−(f(x₁)/f′(x₁)). In the example of FIG. 2, the indexselector 218 rounds the calculated third index to a nearest wholenumber.

The example angle calculator 220 calculates a third tangent line (e.g.,for calculating the third tuple value and/or the third angle) bycalculating a value y₂ of the signature function f(x) at the third index(x₂) (e.g., y₂=f(x₂)). The example angle calculator 220 also calculatesa value of the derivative function f′(x) (i.e., the slope of the linetangent to the signature function f(x)) at the third index (x₂) (e.g.,y′₂=f′(x₂)). The third tangent line is a line that has a value equal tothe value of the signature function f(x) at the third index (e.g.,y₂=f(x₂)) and that has a slope equal to the derivative function f′(x) atthe third index e.g., y′₂=f′(x₂)).

In the example of FIG. 2, the example index selector 218 calculates afourth index value (x₃) as the index value (x_(n)) at which the thirdtangent line is equal to zero. For example, the index selector 218calculates the fourth index value (x₃) asx₃=x₂−(y₂/y′₂)=x₂−(f(x₂)/f′(x₂)). In the example of FIG. 2, the indexselector 218 rounds the calculated fourth index to a nearest wholenumber.

When the first, second, and third tangent lines are calculated, theexample angle calculator 220 determines a first angle (e.g., in degrees)between the first tangent line and the reference line, a second angle(e.g., in degrees) between the second tangent line and the referenceline, and a third angle (e.g., in degrees) between the third tangentline and the reference line. The example angle calculator 220 calculatesthe first angle (e.g., the first tuple value q) asq=(−y₀)/(x₁−x₀)*(180/π). The example angle calculator 220 calculates thesecond angle (e.g., the second tuple value r) asr=(−y₁)/(x₂−x₁)*(180/π). The example angle calculator 220 calculates thethird angle (e.g., the third tuple value s) as s=(−y₂)/(x₃−x₂)*(180/π).

The example tuple generator 210 generates the tuple as an ordered set ofthe angles (e.g., [q, r, s]). The tuple generator 210 outputs the tuple(q, r, s) as a signature for the audio block. The example signaturegenerator 212 of FIG. 2 includes the audio block signature as a tuple ina set of tuples making up a signature for an audio item. In the exampleof FIG. 2, the audio item includes a set of sequential audio blocks. Insome examples, the audio blocks are sampled such that the audio blockspartially overlap. In some other examples, the audio blocks do notoverlap.

In some examples, the tuple for an audio block is further compressed byaveraging the angles in the tuple to obtain a single value. Suchcompression is advantageous for signature storage and computationalefficiency of signature comparison. However, such compression may resultin increased false positives when matching signatures. False positivesmay be mitigated by adjusting a correlation threshold for determiningmatches between signatures and/or portions of signatures.

In some examples, the signature generator 212 includes a signaturereducer 222 to further reduce the signature of the audio to a binaryvalue that may be used, for example, to compare signatures using aHamming distance. For example, as the tuple generator 210 generatestuples (e.g., sets of angles), the example signature reducer 222collects the tuples in a local buffer 224 until a designated number oftuples are stored (e.g., 32 tuples, 64 tuples, or any other number). Forexample, the signature reducer 222 may reduce a 3-tuple to a singlevalue by determining the mean of the value (e.g., angles) in the3-tuple, and stores the single value as representative of the 3-tuple inthe local buffer 224.

Continuing with the example, when the designated number of tuples isstored in the local buffer 224, the example signature reducer 222calculates a statistically-descriptive value (e.g., a mean value, amedian value, etc.) of the tuples stored in the local buffer 224. Theexample signature reducer 222 compares each of the tuple values to thestatistically-descriptive value (e.g., the mean value) to determine abit representative of the tuple. For example, the signature reducer 222may set the bit corresponding to the tuple to be ‘1’ when the tuple isless than the statistically-descriptive value (e.g., the mean value) and‘0’ when the tuple is greater than or equal to thestatistically-descriptive value. The example signature reducer 222therefore reduces X tuples stored in the local buffer 224 to an X-bitbinary signature. For example, if 64 tuples are used, the examplesignature reducer 222 may generate a 64-bit binary number (e.g., a‘long’ number, as used in computer programming).

In some examples, such as for generating a query signature, aftergenerating a signature for a set of tuples in the local buffer 224, theexample signature reducer 222 clears the local buffer 224 and stores asecond set of tuples, which do not overlap with the previous set oftuples, to generate a second signature.

Additionally or alternatively, after generating a signature number forthe tuples in the local buffer 224, the example signature reducer 222may obtain another tuple value and replace an earliest tuple in thelocal buffer with the most recent tuple value (e.g., afirst-in-first-out replacement scheme). The signature reducer 222 thencalculates another binary signature for the tuples stored in the localbuffer 224. For example, the signature reducer 222 may generate a first64-bit signature value for tuples 0 to 63, generate a second 64-bitsignature value for tuples 1 to 64, generate a third 64-bit signaturevalue for tuples 2 to 65, and so on.

A numerical example of generating a tuple is described below. Thenumbers in the example below are truncated for brevity. In this example,the curve fitter 208 calculates a signature functionf(x)=0.0000001131x²−0.0000798769x+0.01189027 (e.g., from a set ofenergy-compacted frequency bands) and a resulting derivative functionf′(x)=0.0000002263x−0.0000798769. The example index selector 218 selectsthe initial index (x₀) to be x₀=−1.

Using the initial index (x₀), the example angle calculator 220determines a first value of signature function f(x₀) to bef(1)=0.0000001131*(1)²−0.0000798769*(1)+0.01189027=0.01181050621782. Theexample angle calculator 220 further determines the first derivativevalue f′(x₀) to be f′(1)=0.0000002263*(1)−0.0000798769=−0.0000796506.

The example index selector 218 calculates the second index x₁ asx₁=x₀−[f(x₀)/f′(x₀)]=1−(0.0118105062/−0.0000796506)=149.27. The exampleindex selector 218 of FIG. 2 rounds the calculated second index, 149.27,down to the whole number, or x₁=149.

The example angle calculator 220 of FIG. 2 determines a second value ofsignature function f(x₁) to bef(149)=0.0000001131*(149)²−0.0000798769*(149)+0.01189027=0.0025006463.The example angle calculator 220 further determines the first derivativevalue f′(x₁) to be f′(149)=0.000000226*(149)−0.0000798769=−0.0000461583.

The example index selector 218 calculates the third index x₂ asx₂=x₁−[f(x₁)/f′(x₁)]=149−(0.0025006463/−0.0000461583)=203.17. Theexample index selector 218 of FIG. 2 rounds the calculated third index203.17 down to the whole number, or x₂=203.

The example angle calculator 220 of FIG. 2 determines a third value ofsignature function f(x₂) to bef(203)=0.0000001131*(203)²−0.0000798769*(203)+0.01189027=0.0003380437.The example angle calculator 220 further determines the third derivativevalue f′(x₂) to bef′(203)=0.0000002263*(203)−0.000079876932=−0.0000339381.

The example index selector 218 calculates the fourth index x₃ asx₃=x₂−[f(x₂)/f′(x₂)]=203−(0.0003380437/−0.0000339381)=212.96. Theexample index selector 218 of FIG. 2 rounds the calculated third index212.96 down to the whole number, or x₂=212.

The example angle calculator 220 of FIG. 2 calculates the first angle(q) in the tuple (q, r, s) asq=(−y₀)/(x₁−x₀)*(180/π)=(−0.0118105062)/(149−1)*(180/π)=−0.0045722443degrees. The example angle calculator 220 of FIG. 2 calculates thesecond angle (r) in the tuple (q, r, s) asr=(−y₁)/(x₂−x₁)*(180/π)=(−0.0025006463))/(203−149)*(180/π)=−0.0026532681degrees. The example angle calculator 220 of FIG. 2 calculates the thirdangle (s) in the tuple (q, r, s) ass=(−y₁)/(x₂−x₁)*(180/π)=(−0.0003380437))/(212−203)*(180/π)=−0.0021520533degrees.

The example signature generator 212 of FIG. 2 adds the tuple(−0.0045722443, −0.0026532681, −0.0021520533) to a signature for theaudio item from which the audio block was sampled. For media having aduration, the example signature generator 212 associates the generatedtuple with a time (e.g., a time indexed to an initial time)corresponding to the first sample in the audio block (e.g., a timerelative to the start of the media item). The signature for an audioitem may be, for example, an ordered set of tuples (T₀, T₁, T₂, T₃, . .. ) corresponding to the order of the blocks of samples obtained fromthe input signal.

While the example tuple generator 210 described above generates tuplesto include angles, the example tuple generator 210 may additionally oralternatively generate tuple values using other aspects of the signaturefunction f(x), such as index values calculated using the tangent linesor other methods based on the signature function (e.g., truncated indexvalues, rounded index values, or unmodified calculated index values),ratios of values of the signature function at selected indices, and/orany other values descriptive of the signature function f(x).

After generating a complete signature for a media item (e.g., generatinga tuple for each audio block in the media item), and/or after generatinga signature for a period of time (e.g., a signature of a minute ofmedia, a signature of 30 seconds of media, a signature of 1 hour ofmedia, and/or for any other period of time), the example signaturegenerator 212 outputs the signature to be stored and/or transmitted.

FIG. 3 is a block diagram of an example signature comparator 300 thatmay be used to implement the example signature analyzer 132 of FIG. 1.The example signature comparator 300 of FIG. 3 includes a referencesignature windower 302, a query signature windower 304, a correlationcalculator 306, a threshold comparator 308, a signature match log 310,and a reference signature database 312. In general, the examplesignature comparator 300 of FIG. 3 compares a signature of query audioto signature(s) of reference audio to determine whether a matchingthreshold is satisfied between query and reference signatures.

The example reference signature windower 302 and the example querysignature windower 304 define portions of a reference signature and aquery signature, respectively, that are to be compared. In some examplesin which the media to be compared has clearly-defined boundaries (e.g.,a signature of a complete song is to be compared to a reference song),the entire set of tuples making up the query signature may be comparedto an entire set of tuples making up the reference signature.

In other examples, in which the length of the media item and/or thelength of the reference media are unknown, a portion of the querysignature may be selected for comparison with a portion of the referencesignature. In some examples, portions of the query signature and thereference signature are selected to represent a selected time periods(e.g., a selected number of tuples). The example reference signaturewindower 302 selects a set of tuples in a reference signature forcomparison with a set of tuples selected from a query signature by thequery signature windower 304.

The example correlation calculator 306 of FIG. 3 calculates acorrelation between the query signature window and the referencesignature window. In the example of FIG. 3, the correlation calculator306 assigns a set of indices (e.g., 1 to N) to the query signaturewindow and the reference signature window, where the query signaturewindow and the reference signature window are aligned on the indices.For example, the first tuples in the query signature window and thereference signature window are assigned to index value 1, the secondtuples in the query signature window and the reference signature windoware assigned to index value 2, and so forth for all of the N tuples inthe query signature window and the reference signature window.

The example correlation calculator 306 of FIG. 3 selects an index andselects a number of tuples M based on the selected index (e.g., startingat the selected index, starting at the next index, etc.). The number ofselected tuples may be a standardized number (e.g., 8, 9, 10, or anyother number) of tuples. The example correlation calculator 306calculates a correlation value (e.g., a Pearson product-momentcorrelation coefficient or other type of correlation) of the selectedquery tuples and the selected reference tuples and stores the resultingcorrelation value as a correlation value corresponding to the selectedindex. The result is a correlation window including the selected tuples(e.g., x+1, x+2, . . . x+M) from each of the reference signature windowand the query signature window.

The example correlation calculator 306 selects a next index (e.g., index2) and repeats the correlation calculation to calculate a secondcorrelation value for another set of reference signature window tuplesand query signature window tuples based on the number of tuples M forgenerated a correlation window. In total, the example correlationcalculator 306 performs the correlation calculation described above forN−M indices. For example, if 100 tuples are included in each of thequery signature window and the reference signature window, and 10 tuples(e.g., x+1, x+2, . . . , x+10) are used for each calculation of acorrelation value, the example correlation calculator 306 calculatescorrelation values for indices 1 to 90, and does not calculatecorrelation values for indices 91 to 100. In some other examples, thecorrelation calculator 306 calculates the correlation values for theindices N−M to N by, for example, reducing the value of M (e.g., using 9tuples for index 91, using 8 tuples for index 92, etc.) and/or usingtuples from outside of the defined reference correlation window and thedefined query correlation window.

The example reference signature windower 302 and/or the query signaturewindower 304 perform sliding windows to compare different windows of thereference signature to different windows of the query signature.

In some examples, the correlation calculator 306 performs a slidingcorrelation of a reference signature window and a query signature windowby adjusting (e.g., incrementing, decrementing) the N indices applied tothe tuples in the query signature window relative to the N indicesapplied in the tuples in the reference signature window. After eachadjustment of the indices, the example correlation calculator 306calculates the correlation values for the reference signature window andthe query signature window using the new assignment of the indices.

After calculating the correlation values for the reference signaturewindow and the query signature window, the example threshold comparator308 determines, for each of the N correlation values (e.g., the N−Mvalues calculated for the reference signature window and the querysignature window), whether an average of the correlation values (e.g.,N−M values) satisfies a threshold correlation (e.g., 0.70, or any otherappropriate threshold). If the average correlation satisfies thecorrelation threshold, the example threshold comparator 308 stores orindicates a match between the query signature window and the referencesignature window.

In some other examples, instead of using the average of the correlationvalues, the example threshold comparator 308 may determine whether anumber (or percentage) of correlation values that satisfy a correlationthreshold (e.g., 0.70, or any other appropriate threshold) satisfies awindow matching threshold (e.g., 80%, or any other appropriatepercentage, and/or an equivalent number of correlation values). As anexample, the threshold comparator 308 may determine whether at least 80%of the correlation values (e.g., N−M values) for a query signaturewindow and a reference signature window are at least 0.70.

The example threshold comparator 308 of FIG. 3 further determineswhether query media matches reference media based on a number ofindividual windows and/or blocks of audio that match. For example, thethreshold comparator 308 may determine, based on a number of matchingwindows indicated in the signature match log 310. For example, thethreshold comparator 308 may determine whether a query audio item (e.g.,a recorded song) matches a reference audio item (e.g., a reference song)based on a number or proportion of windows (e.g., a query signaturewindow matching a reference signature window) identified as matchingbetween the query audio item and the reference audio item.

In some other examples, such as examples in which the signaturegenerator 212 of FIG. 2 reduces a signature to a binary numberrepresentative of a corresponding set of tuples (e.g., an X-bit numberfor X tuples), the example correlation calculator 306 of FIG. 3 comparesthe signatures using other comparison measures, such as Hammingdistances. For example, the correlation calculator 306 may compare aquery signature to successive reference signatures to determine areference signature that has a closest Hamming distance to the querysignature. The example threshold comparator 308 of FIG. 3 determinesthat reference media matches the query media when at least a thresholdnumber or percentage of reference signatures obtained from the referencemedia have a Hamming distance that satisfies a threshold Hammingdistance to the query signatures generated from the query media.

While example manners of implementing the signature generators 114, 136,the reference signature generator 122, and/or the example signatureanalyzer 132 of FIG. 1 are illustrated in FIGS. 2 and 3, one or more ofthe elements, processes and/or devices illustrated in FIGS. 2 and/or 3may be combined, divided, re-arranged, omitted, eliminated and/orimplemented in any other way. Further, the example transducer 202, theexample sampler 204, the example transformer 206, the example curvefitter 208, the example tuple generator 210, the example signaturegenerator 212, the example polyphase quadrature filter 214, the exampleenergy compactor 216, the example index selector 218, the example anglecalculator 220, the example signature reducer 222, the example localbuffer 224, the example reference signature windower 302, the examplequery signature windower 304, the example correlation calculator 306,the example threshold comparator 308, the example signature match log310, the example reference signature database 312 and/or, moregenerally, the example signature generators 114, 122, 136, 200 of FIGS.1 and 2, the example signature analyzer 132 of FIG. 1, and/or theexample signature comparator 300 of FIG. 3 may be implemented byhardware, software, firmware and/or any combination of hardware,software and/or firmware. Thus, for example, any of the exampletransducer 202, the example sampler 204, the example transformer 206,the example curve fitter 208, the example tuple generator 210, theexample signature generator 212, the example polyphase quadrature filter214, the example energy compactor 216, the example index selector 218,the example angle calculator 220, the example signature reducer 222, theexample local buffer 224, the example reference signature windower 302,the example query signature windower 304, the example correlationcalculator 306, the example threshold comparator 308, the examplesignature match log 310, the example reference signature database 312and/or, more generally, the example signature generators 114, 122, 136,200 of FIGS. 1 and 2, the example signature analyzer 132 of FIG. 1,and/or the example signature comparator 300 of FIG. 3 could beimplemented by one or more analog or digital circuit(s), logic circuits,programmable processor(s), application specific integrated circuit(s)(ASIC(s)), programmable logic device(s) (PLD(s)) and/or fieldprogrammable logic device(s) (FPLD(s)). When reading any of theapparatus or system claims of this patent to cover a purely softwareand/or firmware implementation, at least one of the example transducer202, the example sampler 204, the example transformer 206, the examplecurve fitter 208, the example tuple generator 210, the example signaturegenerator 212, the example polyphase quadrature filter 214, the exampleenergy compactor 216, the example index selector 218, the example anglecalculator 220, the example signature reducer 222, the example localbuffer 224, the example reference signature windower 302, the examplequery signature windower 304, the example correlation calculator 306,the example threshold comparator 308, the example signature match log310, the example reference signature database 312 is/are herebyexpressly defined to include a tangible computer readable storage deviceor storage disk such as a memory, a digital versatile disk (DVD), acompact disk (CD), a Blu-ray disk, etc. storing the software and/orfirmware. Further still, the example signature generators 114, 136, theexample reference signature generator 122, and/or the example signatureanalyzer 132 of FIG. 1 may include one or more elements, processesand/or devices in addition to, or instead of, those illustrated in FIGS.2 and/or 3, and/or may include more than one of any or all of theillustrated elements, processes and devices.

FIG. 4 shows an example audio signal 400 including a set of samples 402.

The example audio signal 400 of FIG. 4 is to be converted to a signature(e.g., by the signature generators 114, 122, 136, 200 of FIGS. 1 and/or2) as described in the examples below. The example set of samples 402includes 576 samples. At a sampling rate of 8 kHz, the example samples402 represent 0.072 seconds of a time-domain signal. Other samplingrates may result in a different number of the samples 402 to represent asame time duration (e.g., 0.072 seconds) of the time-domain audio signal400. The example samples 402 of FIG. 4 may be captured by the exampletransducer 202 and/or sampled by the example sampler 204 of FIG. 2.

FIG. 5 shows an example frequency-domain representation 500 of thesamples 402 of the example audio signal 400 of FIG. 4. The examplefrequency-domain representation 500 represents the example samples 402of FIG. 4 after applying a polyphase quadrature filter (e.g., the PQF214 of FIG. 2), energy compaction (e.g., an MDCT via the energycompactor 216 of FIG. 2), and frequency band selection (e.g., via theenergy compactor 216 of FIG. 2). As illustrated in FIG. 5, thefrequency-domain representation 500 includes frequency bands 502 (e.g.,numbered 1 to 107). The numbers of the frequency bands in FIG. 5 may bemapped to frequency ranges. The value of the frequency-domainrepresentation 500 at each of the bands 502 is an energy of theenergy-compacted signal in the frequency band. In some examples, thevalue of the frequency-domain representation 500 is a percentage of theenergy in the audio block represented in the frequency band.

The example curve fitter 208 of FIG. 2 performs curve fitting using thefrequency-domain representation 500 to determine a signature functionrepresentative of the frequency-domain representation 500. FIG. 6 showsan example signature function 600 generated by the example curve fitter208. The example signature function 600 of FIG. 6 is a quadraticfunction (e.g., a second-degree polynomial function) that is determinedusing a least squares error technique with the frequency-domainrepresentation 500 of FIG. 5.

The example signature function 600 is shown in FIG. 6 over a set ofindices 602, where the signature function 600 has a value correspondingto each of the indices over which the signature function 600 is defined.In the example of FIG. 6, the curve fitter 208 calculates the signaturefunction 600 for a selected set of samples, such as the same number ofsamples included in the captured audio block 400 (e.g., 576 samples).

The example tuple generator 210 of FIG. 2 generates a tuple (e.g., a3-tuple) for the audio block 400 using the example signature function600. The example index selector 218 of FIG. 2 selects an initial index604 (e.g., 1). To calculate a first tangent line 606, the example anglecalculator 220 calculates a value 608 of the signature function 600 atthe initial index 604. The example angle calculator 220 calculates theslope of the first tangent line 606 that is tangent to the signaturefunction 600 at the initial index 604 (e.g., by calculating the value ofthe derivative of the signature function 600 at the first index 604).

The example index selector 218 calculates a second index value 610 asthe index value at which the first tangent line 606 is equal to zero. Inthe example of FIG. 6, the index selector 218 rounds the calculatedsecond index 610 to a nearest whole number.

The example angle calculator 220 calculates a second tangent line 612(e.g., for calculating the second tuple value and/or the second angle)by calculating a value 614 of the signature function 600 at the secondindex 612. The example angle calculator 220 calculates the slope of thesecond tangent line 612 that is tangent to the signature function 600 atthe second index 610 (e.g., by calculating the value of the derivativeof the signature function 600 at the second index 610).

In the example of FIG. 6, the example index selector 218 calculates athird index value 616 as the index value at which the second tangentline 612 is equal to zero. In the example of FIG. 2, the index selector218 rounds the calculated third index 616 to a nearest whole number.

The example angle calculator 220 calculates a third tangent line 618(e.g., for calculating the third tuple value and/or the third angle) bycalculating a value 620 of the signature function 600 at the third index616. The example angle calculator 220 calculates the slope of the thirdtangent line 616 that is tangent to the signature function 600 at thesecond index 610 (e.g., by calculating the value of the derivative ofthe signature function 600 at the second index 610).

In the example of FIG. 6, the example index selector 218 calculates afourth index value 622 as the index value at which the third tangentline 618 is equal to zero. In the example of FIG. 6, the index selector218 rounds the calculated fourth index 622 to a nearest whole number.

When the first, second, and third tangent lines 606, 612, 618 arecalculated, the example angle calculator 220 determines a first angle624 (e.g., in degrees) between the first tangent line 606 and areference line 626 (e.g., the x-axis, corresponding to an energy valueof 0, and/or any line parallel to the x-axis), a second angle 628 (e.g.,in degrees) between the second tangent line 612 and the reference line626, and a third angle 630 (e.g., in degrees) between the third tangentline 618 and the reference line 626. The example angle calculator 220calculates the first angle (e.g., the first tuple value q) asq=(−1)*(the value 608 of the signature function 600 at the initial index604)/(second index 610−initial index 604)*(180/π). The example anglecalculator 220 calculates the second angle (e.g., the second tuple valuer) as r=(−1)*(the value 614 of the signature function 600 at the secondindex 610)/(third index 616−second index 610)*(180/π). The example anglecalculator 220 calculates the third angle (e.g., the third tuple values) as s=(−1)*(the value 620 of the signature function 600 at the thirdindex 616)/(fourth index 622−third index 616)*(180/π).

The example tuple generator 210 generates the 3-tuple as an ordered setof the angles (e.g., [q, r, s]). The tuple generator 210 outputs thetuple (q, r, s) as a signature for the audio block 400 of FIG. 4. Theexample signature generator 212 of FIG. 2 includes the audio blocksignature as a tuple in a set of tuples making up a signature for anaudio item. As mentioned above, the tuple may be generated using othervalues representative of the signature function f(x), such as indexvalues, ratios of values of the signature function f(x) at selectedindices, etc.

FIG. 7 shows example signature functions 702, 704, 706, 708 resultingfrom different effects on a same block of audio. FIG. 7 furtherillustrates example tuples 710, 712, 714, 716 (e.g., sets of 3 angles)calculated for each of the signature functions 702-708 in accordancewith the examples disclosed above in the example of FIG. 6.

The example signature function 702 represents an audio block obtainedfrom a digital audio file. The digital audio file from which thesignature function 702 is generated is a base file from which the otheraudio blocks corresponding to the signature functions 704-708 aregenerated. The example signature function 704 represents an audio blockinput via a wired line-in connection to the transducer 202 and/or thesampler 204 of FIG. 2. The example signature function 706 represents anaudio block input via a microphone (e.g., a microphone implementing thetransducer 202). The example signature function 708 represents an audioblock input via a digital audio file created by modifying the originalaudio file to have enhanced bass and treble frequencies.

As shown in FIG. 7, the signature functions 702-708 have similar values,have similar locations of their respective minima (e.g., the lowestpoints on the signature functions 702-708), and have similar ranges ofvalues over the set of indices for which the signature functions 700 aredefined in FIG. 7. The example signature function 706 (e.g., input viathe microphone) is the least similar to the example signature function702. However, because matches are calculated using combinations oftuples, the example signature function 706 using the microphone areidentifiable using the example methods and apparatus disclosed herein.In general, the angles resulting from higher audio volumes are larger(e.g., farther from 0) than lower audio volumes of the same audio.However, because the differences are consistent, the example correlationcalculator 306 still identifies sufficiently high correlations betweenaudio of different volumes, enabling matching.

FIG. 8A shows example angles 802 calculated for a set of signatures fora corresponding set of audio blocks in a first audio item. FIG. 8B showsexample angles 804 calculated for a set of signatures for acorresponding set of audio blocks for a second audio item different thanthe first audio item. A comparison of the angles 802, 804 in FIGS. 8A,8B for the different audio items demonstrates that different audio itemsresult in significantly different sets of angles, such that performing asliding correlation (e.g., via the signature comparator 300 of FIG. 3)of the angles 802 and the angles 804 results in a correlation value thatis less than a threshold and can be used to determine that the audioitems do not match.

FIG. 9 shows an example query signature window 902 of a first audio itemand an example reference signature 904 for comparison. For example, thequery signature window 902 may be a windowed portion of a larger set oftuples making up a query signature. Similarly, the reference signaturewindow 904 may be a windowed portion of a larger set of tuples making upa reference signature. FIG. 10 shows example correlation values 1002calculated for the example query signature window 902 and the examplereference signature window 904 of FIG. 9. The example query signaturewindow 902 and the example reference signature window 904 of FIG. 9represent a same audio item.

The example query signature windower 304 of FIG. 3 selects the examplequery signature window 902 as a subset of tuples from a larger set oftuples in a query signature. Similarly, the example reference signaturewindower 302 of FIG. 3 selects the example reference signature window904 of FIG. 9 as a subset of tuples from a larger set of tuples in areference signature.

The example correlation calculator 306 of FIG. 3 assigns indices (e.g.,indices 1 to 69) to the example query signature window 902 and theexample reference signature window 904. As a result of assigning theindices, the example query signature window 902 and the examplereference signature window 904 correspond to the indices as illustratedin FIG. 9.

The example correlation calculator 306 selects a first index (e.g.,index 1) and calculates a correlation value 1002 for the selected index.In the example of FIGS. 9 and 10, the correlation calculator 306 uses 10tuples (e.g., shown in a correlation window 906 in FIG. 9) from each ofthe query signature window 902 and the reference signature window 904 tocalculate the correlation value 1002 at the selected index. The examplecorrelation calculator 306 stores the resulting correlation value 1002for the selected index and iterates the calculation for the subsequentindices (e.g., by selecting additional sets or windows of tuples).

When the correlation calculator 306 has calculated the correlationvalues 1002 for all of the indices (e.g., 1 to 69), the examplethreshold comparator 308 of FIG. 3 determines whether at least athreshold percentage of the 69 correlation values 1002 is greater than athreshold correlation (e.g., a threshold 1004 in FIG. 10). In theexample of FIG. 10, all of the correlation values 1002 are greater thanthe threshold 1004 and, therefore, the example threshold comparator 308determines that the query signature window 902 matches the referencesignature window 904 of FIG. 9.

Flowcharts representative of example machine readable instructions forimplementing the signature generator 200 of FIG. 2 and/or the signaturecomparator 300 of FIG. 3 are shown in FIGS. 11, 12, 13, and 14A-14C. Inthis example, the machine readable instructions comprise program(s) forexecution by a processor such as the processor 1512 shown in the exampleprocessor platform 1500 discussed below in connection with FIG. 15. Theprogram(s) may be embodied in software stored on a tangible computerreadable storage medium such as a CD-ROM, a floppy disk, a hard drive, adigital versatile disk (DVD), a Blu-ray disk, or a memory associatedwith the processor 1512, but the entire program(s) and/or parts thereofcould alternatively be executed by a device other than the processor1512 and/or embodied in firmware or dedicated hardware. Further,although the example program(s) are described with reference to theflowcharts illustrated in FIGS. 11, 12, 13, and 14A-14C, many othermethods of implementing the example signature generator 200 of FIG. 2and/or the signature comparator 300 of FIG. 3 may alternatively be used.For example, the order of execution of the blocks may be changed, and/orsome of the blocks described may be changed, eliminated, or combined.

As mentioned above, the example processes of FIGS. 11, 12, 13, and14A-14C may be implemented using coded instructions (e.g., computerand/or machine readable instructions) stored on a tangible computerreadable storage medium such as a hard disk drive, a flash memory, aread-only memory (ROM), a compact disk (CD), a digital versatile disk(DVD), a cache, a random-access memory (RAM) and/or any other storagedevice or storage disk in which information is stored for any duration(e.g., for extended time periods, permanently, for brief instances, fortemporarily buffering, and/or for caching of the information). As usedherein, the term tangible computer readable storage medium is expresslydefined to include any type of computer readable storage device and/orstorage disk and to exclude propagating signals and transmission media.As used herein, “tangible computer readable storage medium” and“tangible machine readable storage medium” are used interchangeably.Additionally or alternatively, the example processes of FIGS. 11, 12,13, and 14A-14C may be implemented using coded instructions (e.g.,computer and/or machine readable instructions) stored on anon-transitory computer and/or machine readable medium such as a harddisk drive, a flash memory, a read-only memory, a compact disk, adigital versatile disk, a cache, a random-access memory and/or any otherstorage device or storage disk in which information is stored for anyduration (e.g., for extended time periods, permanently, for briefinstances, for temporarily buffering, and/or for caching of theinformation). As used herein, the term non-transitory computer readablemedium is expressly defined to include any type of computer readablestorage device and/or storage disk and to exclude propagating signalsand transmission media. As used herein, when the phrase “at least” isused as the transition term in a preamble of a claim, it is open-endedin the same manner as the term “comprising” is open ended.

FIG. 11 is a flowchart representative of example computer readableinstructions 1100 which may be executed to implement the examplesignature generator 114, the example reference signature generator 122,and/or the example signature generator 200 of FIGS. 1 and/or 2 togenerate an audio signature.

The example transducer 202 of FIG. 2 captures audio (block 1102). Forexample, a microphone transducer may transform ambient audio into arepresentative electrical signal. The example sampler 204 of FIG. 2samples the audio to create an audio block (e.g., a block of audiosamples) (block 1104).

The example transformer 206 of FIG. 2 transforms the audio block from atime-domain representation to a frequency-domain representation havingfrequency bands (block 1106). For example, the PQF 214 of FIG. 2transforms the time-domain signal into a frequency-domain representationand the energy compactor 216 applies an energy compaction technique(e.g., an MDCT) to compact the energy of the frequency-domainrepresentation into a smaller number of frequency bands. The result ofblock 1106 is an energy-compacted frequency-domain representation of thesampled audio signal. Example instructions to implement block 1106 aredisclosed below with reference to FIG. 12.

The example transformer 206 selects a subset of the frequency bands inthe frequency-domain representation (block 1108). For example, thetransformer 206 may select a set of frequency bands representing atleast a threshold portion of the energy in the energy-compactedfrequency-domain representation.

The example tuple generator 210 of FIG. 2 creates a tuple representingthe audio block (block 1110). For example, the tuple generator 210generates a set of values (e.g., an ordered set of 3 values) bydetermining characteristic values from a function that represents theselected set of frequency bands. Example instructions to implement block1110 are disclosed below with reference to FIG. 13.

The example signature generator 212 of FIG. 2 adds the generated tupleto an audio signature (block 1112). For example, the signature generator212 adds the tuple to an ordered set of tuples representing a sequenceof audio blocks. The example sampler 204 determine whether there isadditional audio to be sampled (block 1114). For example, the sampler204 may determine whether energy in the electrical signal generated bythe transducer 202 exceeds a threshold (e.g., indicating that ambientaudio is still being received with at least a threshold energy level).Additionally or alternatively, the sampler 204 may determine whether alimit or other cutoff condition has occurred to delineate one audio itemfrom another. For example, the sampler 204 may split a continuous streamof audio into multiple audio items. If there is additional audio (block1114), control returns to block 1104.

When there is no additional audio (block 1114), the example signaturegenerator 212 of FIG. 2 stores the audio signature including the orderedset of tuples (block 1116). For example, the signature generator 212 maystore a data set including the values of the tuples in a storage devicefor later transmission and/or analysis.

The example signature generator 212 determines whether to send audiosignatures for matching (block 1118). For example, the signaturegenerator 212 may be configured to periodically or aperiodically (e.g.,in response to a request, when a storage size of the audio signaturessatisfies a threshold, etc.) send the stored audio signatures to amatching entity (e.g., the central data collection facility 106 ofFIG. 1) for matching to reference audio.

If the signature generator 212 determines that it is not to send theaudio signatures for matching (block 1118), control returns to block1102 to continue capturing audio. When the signature generator 212determines that it is to send the audio signatures for matching (block1118), the example signature generator 212 transmits the audiosignatures to a central matching facility (e.g., the central datacollection facility 106) for matching the audio signatures to referencesignatures (block 1120). For example, the signature generator 212 maytransmit a data file including the audio signatures to the examplecentral data collection facility 106 via the network 108 of FIG. 1.

The example instructions 1100 of FIG. 11 end. In some examples, thesignature generator 200 of FIG. 2 iterates the instructions 1100 torepeatedly (e.g., continuously) generate audio signatures of input audio(e.g., ambient audio).

FIG. 12 is a flowchart representative of example computer readableinstructions 1200 which may be executed to implement the exampletransformer 206 of FIG. 2 to transform a block of audio into afrequency-domain representation. For example, the transformer 206 ofFIG. 2 may implement the instructions 1200 of FIG. 12 to convert theexample audio signal 400 of FIG. 4, from the time-domain representationincluding the samples 402, to an energy-compacted frequency-domainrepresentation 500 shown in FIG. 5. The example instructions 1200 ofFIG. 12 may be performed by the example transformer 206 to implementblock 1106 of FIG. 11.

The example PQF 214 of FIG. 2 transforms time-domain samples tofrequency-domain samples using a polyphase quadrature filter (block1202). The PQF 214 is a type of filter bank that uses a set of band-passfilters to separate an input signal into multiple components. The outputof block 1202 is a set of frequency bands and corresponding energiesbased on the energy content of the frequencies in the time-domainsignal.

The example energy compactor 216 of FIG. 2 performs energy compaction onthe frequency-domain samples using a MDCT to obtain energy-compactedfrequency bands (block 1204). The MDCT causes the energy in thefrequency-domain representation output by the PQF 214 to be concentratedin a smaller number of frequency bands. Thus, the example energycompactor 216 increases the compression of the audio signal.

The example instructions 1200 of FIG. 12 end and control is transferredto block 1108 of FIG. 11.

FIG. 13 is a flowchart representative of example computer readableinstructions 1300 which may be executed to implement the example tuplegenerator 210 of FIG. 2 to generate a tuple for a block of audio. Theexample tuple generator 210 may perform the example instructions 1300 ofFIG. 13 to implement block 1110 of FIG. 11. The example instructions1300 of FIG. 13 are performed subsequent to the transformer 206 of FIG.2 selecting a set of frequency bands (e.g., block 1108 of FIG. 11), andwill be described below with reference to the example signature function600 of FIG. 6.

The example curve fitter 208 of FIG. 2 calculates a signature functionf(x) (e.g., the signature function 600 of FIG. 6) corresponding to theselected frequency bands in the frequency-domain representation of themedia signal (block 1302). For example, the curve fitter 208 generatesthe signature function f(x) as a quadratic function (e.g., asecond-order function). In other examples, other orders of functions maybe used. Using an example notation of the signature functionf(x)=ax²+bx+c, the example curve fitter 208 of FIG. 2 determines thecoefficients a, b, and c of the signature function. In some examples,the curve fitter 208 uses, for example, the least squares errortechnique to determine the coefficients (a, b, c) of the signaturefunction f(x).

The example curve fitter 208 calculates a derivative function f′(x) ofthe signature function f(x) (block 1304). For example, the derivativefunction f(x) is a linear function (e.g., f′(x)=2ax+b) when the examplesignature function f(x) is a quadratic function.

The example index selector 218 of FIG. 2 selects an initial index x₀(e.g., the initial index 604 of FIG. 6) (block 1306). In some examples,the initial index x₀ is a standardized value, such as x₀=1, that isselected for the generation of every tuple in a signature. In some otherexamples, the index selector 218 calculates the initial index (x₀) usinga formula that is based on one or more aspects of the signature functionf(x). For example, the index selector 218 may select the initial index(x₀) to be a closest index value (x_(n)) to a maximum value of thesignature function f(x) within the range in which the curve fitter 208has defined the signature function f(x).

The example angle calculator 220 calculates a first value y₀ (e.g., thevalue 608 of FIG. 6) of the signature function f(x) at the initial indexx₀ (e.g., y₀=f(x₀)) (block 1308). For example, the angle calculator 220evaluates the value y₀ of the signature function f(x) at the initialindex x₀.

The example angle calculator 220 calculates a first value y′₀ of thederivative function f′(x) (i.e., the slope of the first tangent line 606of FIG. 6) at the initial index x₀ (e.g., y′₀=f′(x₀)) (block 1310). Thefirst tangent line 606 is a line that has a value equal to the value ofthe signature function f(x) at the first index (e.g., y₀=f(x₀)) and thathas a slope equal to the derivative function f′(x) at the first indexe.g., y′₀=f(x₀)).

The example index selector 218 calculates a second index value x₁ (e.g.,the second index 610 of FIG. 6) as x₁=x₀−(y₀/y′₀)=x₀−(f(x₀)/f′(x₀))(block 1312). For example, the second index value x₁ is the index valuex_(n) at which the first tangent line 606 is equal to zero. In theexample of FIG. 2, the index selector 218 rounds the calculated secondindex x₁ to a nearest whole number.

The example angle calculator 220 calculates a second value y₁ (e.g., thevalue 614 of FIG. 6) of the signature function f(x) at the second indexx₁ (e.g., y₁=f(x₁)) (block 1314). The example angle calculator 220 alsocalculates a value y′₁ of the derivative function f′(x) (i.e., the slopeof the second tangent line 612 of FIG. 6 at the second index x₁,y′₁=f′(x₁)) (block 1316). The second tangent line 612 is a line that hasa value equal to the value of the signature function f(x) at the secondindex (e.g., y₁=f(x₁)) and that has a slope equal to the derivativefunction f′(x) at the second index e.g., y′₁=f′(x₁)).

In the example of FIG. 2, the example index selector 218 calculates athird index value x₂ (e.g., the third index 616 of FIG. 6) asx₂=x₁−(y₁/y′₁)=x₁−(f(x₁)/f′(x₁)) (block 1318). For example, the thirdindex value x₂ is the index value x_(n) at which the second tangent line612 is equal to zero. In the example of FIG. 2, the index selector 218rounds the calculated third index to a nearest whole number.

The example angle calculator 220 calculates a third value y₂ (e.g., thevalue 620 of FIG. 6) of the signature function f(x) at the third indexx₂ (e.g., y₂=f(x₂)) (block 1320). The example angle calculator 220 alsocalculates a value y′₂ of the derivative function f′(x) (i.e., the slopeof the third tangent line 618) at the third index x₂ (e.g., y′₂=f′(x₂))(block 1322). The third tangent line 618 is a line that has a valueequal to the value of the signature function f(x) at the third index(e.g., y₂=f(x₂)) and that has a slope equal to the derivative functionf′(x) at the third index e.g., y′₂=f′(x₂)).

In the example of FIG. 2, the example index selector 218 calculates afourth index value x₃ (e.g., the fourth index 622 of FIG. 6) asx₃=x₂−(y₂/y′₂)=x₂−(f(x₂)/f′(x₂)) (block 1324). For example, the fourthindex value x₃ is the index value x_(n) at which the third tangent line618 is equal to zero. In the example of FIG. 2, the index selector 218rounds the calculated fourth index to a nearest whole number.

The example angle calculator 220 determines a first angle S₀ (e.g., theangle 624 of FIG. 6, in degrees) between the first tangent line 606 anda reference line (e.g., the reference line 626 of FIG. 6) asS₀=(−y₀)/(x₁−x₀)*(180/π) (block 1326).

The example angle calculator 220 determines a second angle S₁ (e.g., theangle 628 of FIG. 6, in degrees) between the second tangent line 612 andthe reference line 626 as S₁=(−y₁)/(x₂−x₁)*(180/π) (block 1328).

The example angle calculator 220 determines a third angle S₂ (e.g., theangle 630 of FIG. 6, in degrees) between the third tangent line 618 andthe reference line 626 as S₂=(−y₂)/(x₃−x₂)*(180/π) (block 1330).

The example tuple generator 210 generates the tuple as an ordered set ofthe angles (e.g., [S₀, S₁, S₂]) (block 1332). The example instructions1300 then end and return control to block 1112 of FIG. 11 to add thetuple (e.g., [S₀, S₁, S₂]) to an audio signature.

FIGS. 14A, 14B, and 14C collectively show a flowchart representative ofexample computer readable instructions 1400 which may be executed toimplement the example signature analyzer 132 and/or the examplesignature comparator 300 of FIG. 3 to match a query signature to areference signature. For example, the instructions 1400 may be used toidentify query media, such as audio, by matching signatures of the querymedia to signatures of the reference media.

The example signature comparator 300 of FIG. 3 receives a querysignature for comparison (block 1402). For example, the query signaturewindower 304 of FIG. 3 may receive a query signature from a signaturegenerator such as the signature generator 114 of FIG. 1.

The example reference signature windower 302 of FIG. 3 selects areference signature for comparison with the query signature (block1404). For example, the reference signature windower 302 may query thereference signature database 312 of FIG. 3 based on one or morecharacteristics of the query signature to select a potential matchingreference signature.

The example correlation calculator 306 of FIG. 3 selects a number oftuples for a correlation window (block 1406). For example, thecorrelation calculator 306 may use a same number of tuples for eachcorrelation window and/or may vary a number of tuples based on one ormore characteristics of the query signature and/or the referencesignature.

The example query signature windower 304 of FIG. 3 selects a portion ofthe query signature and applies a window function to generate a querysignature window (e.g., the query signature window 902 of FIG. 9) (block1408). For example, the window function may include a number of tuplesin the query signature and exclude the remainder of the tuples.

The example reference signature windower 302 of FIG. 3 selects a portionof the reference signature and applies the window function to generate areference signature window (e.g., the reference signature window 904 ofFIG. 9) (block 1410). For example, the reference signature windower 302uses the same window used by the query signature windower 304 in block1408 to generate a reference signature window 904 having the same numberof tuples as the query signature window 902.

The example correlation calculator 306 assigns indices to the querysignature window 902 and the reference signature window 904 (block1411). For example, the correlation calculator 306 may assign sequentialindices to corresponding ones of the tuples in the query signaturewindow 902 and the reference signature window 904, such as index 1 tothe first tuples in the query signature window 902 and the referencesignature window 904, index 2 to the second tuples in the querysignature window 902 and the reference signature window 904, and so on.

The example correlation calculator 306 of FIG. 3 selects an index forcorrelation (block 1412). For example, the correlation calculator 306selects one of the indices assigned to the tuples in the query signaturewindow 902 and the reference signature window 904.

The example correlation calculator 306 determines a query correlationwindow (e.g., the tuples of the query signature window 902 within thecorrelation window 906 of FIG. 9) from the selected index and theselected number of tuples (block 1414). For example, if the selectedindex (from block 1412) is ‘1’ and the selected number of tuples (fromblock 1406) is 10, the example correlation calculator 306 determines thequery correlation window to include 10 tuples (e.g., a sequential set oftuples) starting at an index based on index 1 (e.g., starting at index1, starting at index 2, etc.). For example, the correlation calculator306 may determine the query correlation window of FIG. 9 from an initialindex (e.g., 1) and a selected number of tuples (e.g., 10 tuples).Similarly, the example correlation calculator 306 determines a referencecorrelation window (e.g., the tuples of the reference signature window904 within the correlation window 906 of FIG. 9) from the selected indexand the selected number of tuples (block 1416). For example, thereference correlation window may be determined in the same manner usedto determine the query correlation window.

The example correlation calculator 306 determines a correlation value(e.g., a correlation value 1002 of FIG. 10) for the selected index as acorrelation between the query correlation window and the referencecorrelation window (block 1418). For example, the correlation calculator306 may determine a correlation coefficient (e.g., the Pearsonproduct-moment correlation coefficient and/or any other type ofcorrelation) between the set of tuples of the query correlation windowand the set of tuples of the reference correlation window.

The example correlation calculator 306 determines whether the selectedindex is the final index in the query signature window (block 1420). Forexample, the correlation calculator 306 may determine whethercorrelation values can be calculated for additional indexes of the querysignature window based on the selected number of tuples for thecorrelation window. If, for example, the selected number of tuples is10, and correlation values have been calculated for indices 1 through 90of query signature window having 100 tuples, the example correlationcalculator 306 may determine that the selected index is the final indexbecause the 91^(st) index does not have 10 tuples available from thequery signature window to calculate the correlation value for the91^(st) index (without including additional tuples from the querysignature beyond those included in the query correlation window). If theselected index is not the final index in the query signature window(e.g., there are additional indices for which a correlation value can becalculated) (block 1420), the example correlation calculator 306increments the index for correlation (block 1422) and returns control toblock 1414 to determine another query correlation window.

When the selected index is the final index in the query signature window(block 1420), the example threshold comparator 308 of FIG. 3 calculatesa percentage of the calculated correlation values that satisfy acorrelation threshold value (block 1424). For example, the thresholdcomparator 308 compares each of the example correlation valuescalculated by the correlation calculator 306 (e.g., correlation valuescorresponding to the indices and/or corresponding to the correlationwindows) to a correlation threshold (e.g. 0.7, or another appropriatevalue between −1.0 and +1.0, for Pearson product-moment correlationcoefficients).

The example threshold comparator 308 determines whether the percentageof the correlation values that satisfy the threshold (block 1424) forthe selected reference signature window and the selected query windowsatisfies a matching threshold (block 1426). The correlation thresholdand/or the matching threshold may be selected to identify a match whenthe signal underlying the query signature is qualitatively the same asthe reference signal underlying the reference signature. The correlationthreshold and/or the matching threshold are also selected to reduce(e.g., avoid) false positives (e.g., to reduce the instances ofindicating a match between two signals when the signals would not berecognized as the same by a human observer).

If the percentage of the correlation values for the selected referencesignature window and the selected query window satisfies a matchingthreshold (block 1426), the example threshold comparator 308 logs amatch between the selected reference window and the selected querywindow (block 1428). For example, the threshold comparator 308 may storean indication of the match in the signature match log 310 of FIG. 3.

If the percentage of the correlation values for the selected referencesignature window and the selected query window does not satisfy amatching threshold (block 1426), the example reference signaturewindower 302 determines whether there are additional portions of thereference signature for comparison with the query signature (block1430). If there are additional portions of the reference signature forcomparison with the query signature (block 1430), the example referencesignature windower 302 returns control to block 1410 to generate anotherreference signature window.

When there are no more portions of the reference signature forcomparison with the query signature (block 1430), or after logging amatch between the selected reference window and the selected querywindow (block 1428), the example query signature windower 304 of FIG. 3determines whether there are additional portions of the query signaturefor comparison (block 1432). For example, if a query signature window isnot matched to a reference signature window, the example query signaturewindower 304 may generate another query signature window that partiallyoverlaps the non-matching query signature window. Conversely, if a querysignature window is matched to a reference signature window, the examplequery signature windower 304 may generate another query signature windowthat has no overlapping samples with the matched query signature window.

If there are additional portions of the query signature for comparison(block 1432), the example query signature windower 304 to block 1408 toselect another portion of the query signature.

When there are no more portions of the query signature for comparison(block 1432), the example threshold comparator 308 determines whetherthe percentage of matches between the query signature windows and thereference signature windows for the selected reference signature satisfya threshold (block 1434). For example, the threshold comparator 308 maydetermine how much of the query signature (e.g., the non-overlappingpercentage of the query signature) has been matched to the referencesignature.

If the percentage of matches between the query signature windows and thereference signature windows for the selected reference signaturesatisfies the threshold (block 1434), the example threshold comparator308 of FIG. 3 logs a match between the query signature and the selectedreference signature (block 1436). For example, the threshold comparator308 may store an indication in the signature match log 310 that thequery signature matches the selected reference signature.

On the other hand, if the percentage of matches between the querysignature windows and the reference signature windows for the selectedreference signature does not satisfy the threshold (block 1434), theexample reference signature windower 302 of FIG. 3 determines whetherthere are additional reference signatures that can be compared to thequery signature to identify a match (block 1438). If there areadditional reference signatures (e.g., reference signatures stored inthe reference signature database 312 of FIG. 3) (block 1438), theexample reference signature windower 302 transfers control to block 1404to select another reference signature.

When there are no more reference signatures (block 1438), or afterlogging a match between the query signature and the selected referencesignature (block 1436), the example instructions 1400 of FIGS. 14A-14Cend. In some examples, the signature comparator 300 of FIG. 3 repeatsthe instructions 1400 for additional query signatures.

FIG. 15 is a block diagram of an example processor platform 1500 capableof executing the instructions of FIGS. 11, 12, 13, and/or 14A-14C toimplement the example transducer 202, the example sampler 204, theexample transformer 206, the example curve fitter 208, the example tuplegenerator 210, the example signature generator 212, the examplepolyphase quadrature filter 214, the example energy compactor 216, theexample index selector 218, the example angle calculator 220, theexample signature reducer 222, the example local cache 224, the examplereference signature windower 302, the example query signature windower304, the example correlation calculator 306, the example thresholdcomparator 308, the example signature match log 310, the examplereference signature database 312 and/or, more generally, the examplesignature generator 200 of FIG. 2 and/or the example signaturecomparator 300 of FIG. 3. The processor platform 1500 can be, forexample, a server, a personal computer, a mobile device (e.g., a cellphone, a smart phone, a tablet such as an iPad™), a personal digitalassistant (PDA), an Internet appliance, a DVD player, a CD player, adigital video recorder, a Blu-ray player, a gaming console, a personalvideo recorder, a set top box, or any other type of computing device.

The processor platform 1500 of the illustrated example includes aprocessor 1512. The processor 1512 of the illustrated example ishardware. For example, the processor 1512 can be implemented by one ormore integrated circuits, logic circuits, microprocessors or controllersfrom any desired family or manufacturer.

The processor 1512 of the illustrated example includes a local memory1513 (e.g., a cache). The processor 1512 of the illustrated example isin communication with a main memory including a volatile memory 1514 anda non-volatile memory 1516 via a bus 1518. The volatile memory 1514 maybe implemented by Synchronous Dynamic Random Access Memory (SDRAM),Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory(RDRAM) and/or any other type of random access memory device. Thenon-volatile memory 1516 may be implemented by flash memory and/or anyother desired type of memory device. Access to the main memory 1514,1516 is controlled by a memory controller.

The processor platform 1500 of the illustrated example also includes aninterface circuit 1520. The interface circuit 1520 may be implemented byany type of interface standard, such as an Ethernet interface, auniversal serial bus (USB), and/or a PCI express interface.

In the illustrated example, one or more input devices 1522 are connectedto the interface circuit 1520. The input device(s) 1522 permit(s) a userto enter data and commands into the processor 1512. The input device(s)can be implemented by, for example, an audio sensor, a microphone, acamera (still or video), a keyboard, a button, a mouse, a touchscreen, atrack-pad, a trackball, isopoint and/or a voice recognition system.

One or more output devices 1524 are also connected to the interfacecircuit 1520 of the illustrated example. The output devices 1524 can beimplemented, for example, by display devices (e.g., a light emittingdiode (LED), an organic light emitting diode (OLED), a liquid crystaldisplay, a cathode ray tube display (CRT), a touchscreen, a tactileoutput device, a light emitting diode (LED), a printer and/or speakers).The interface circuit 1520 of the illustrated example, thus, typicallyincludes a graphics driver card, a graphics driver chip or a graphicsdriver processor.

The interface circuit 1520 of the illustrated example also includes acommunication device such as a transmitter, a receiver, a transceiver, amodem and/or network interface card to facilitate exchange of data withexternal machines (e.g., computing devices of any kind) via a network1526 (e.g., an Ethernet connection, a digital subscriber line (DSL), atelephone line, coaxial cable, a cellular telephone system, etc.).

The processor platform 1500 of the illustrated example also includes oneor more mass storage devices 1528 for storing software and/or data.Examples of such mass storage devices 1528 include floppy disk drives,hard drive disks, compact disk drives, Blu-ray disk drives, RAIDsystems, and digital versatile disk (DVD) drives.

The coded instructions 1532 of FIGS. 11, 12, 13, and/or 14A-14C may bestored in the mass storage device 1528, in the volatile memory 1514, inthe non-volatile memory 1516, and/or on a removable tangible computerreadable storage medium such as a CD or DVD.

Although certain example methods, apparatus and articles of manufacturehave been disclosed herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe claims of this patent.

1. A method to generate a signature of a signal, comprising:transforming a block of signal samples from a time-domain representationto a frequency-domain representation comprising multiple frequencybands; determining a signature function by fitting a curve to at least asubset of the frequency bands; and calculating signature values for theblock of signal samples by: calculating a first angle between areference line and a first tangent line that is tangent to the signaturefunction at a first index value in a set of index values over which thesignature function is defined; calculating a second angle between thereference line and a second tangent line that is tangent to thesignature function at a second index value in the set of index values;calculating a third angle between the reference line and a third tangentline that is tangent to the signature function at a third index value inthe set of index values; and creating the signature values based on thefirst angle, the second angle, and the third angle.
 2. A method asdefined in claim 1, wherein the first tangent line represents a firstlinear tangent function and the second tangent line represents a secondlinear tangent function.
 3. A method as defined in claim 1, whereinfitting the curve to at least the subset of the frequency bandscomprises performing least squares error analysis to obtain coefficientsfor the signature function to fit at least the subset of the frequencybands.
 4. A method as defined in claim 1, wherein creating the signaturevalues comprises averaging the first angle, the second angle, and thethird angle.
 5. A method as defined in claim 1, further comprisinggenerating a signature for media represented by the block of signalsamples, by: calculating signature values for additional blocks ofsignal samples representing the media; and generating the signature forthe media as an ordered set of the signature values for the blocks ofsignal samples.
 6. A method as defined in claim 5, further comprisingtransmitting the signature to an audience measurement entity.
 7. Amethod as defined in claim 5, wherein generating the signature furthercomprises calculating a mean value of the signature values, andcalculating the signature values comprises determining a signature bitby comparing a mean angle of the first angle, the second angle, and thethird angle to the mean value.
 8. A method as defined in claim 1,wherein calculating the signature values further comprises: selectingthe first index value; calculating the second index value based on afirst value of the signature function at the first index value and aderivative of the signature function at the first index value, thesecond tangent line being determined based on the second index value;and calculating the third index value based on a second value of thesignature function at the second index value and the derivative of thesignature function at the second index value, the third tangent linebeing determined based on the third index value.
 9. A method as definedin claim 1, wherein transforming the block of signal samples comprises:applying a polyphase quadrature filter bank to the block of signalsamples to obtain frequency bands; and applying a modified discretecosine transform to perform energy compaction on the frequency bands togenerate the frequency-domain representation.
 10. A method as defined inclaim 1, further comprising selecting the subset of the frequency bandsin the frequency-domain representation to include a set of adjacent onesof the frequency bands that have at least a threshold percentage of atotal energy in the frequency-domain representation.
 11. An apparatus,comprising: a transformer to transform a block of signal samples from atime-domain representation to a frequency-domain representationcomprising multiple frequency bands; a curve fitter to determining asignature function by fitting a curve to at least a subset of thefrequency bands; an angle calculator to: calculate a first angle betweena reference line and a first tangent line that is tangent to thesignature function at a first index value in a set of index values overwhich the signature function is defined; calculate a second anglebetween the reference line and a second tangent line that is tangent tothe signature function at a second index value in the set of indexvalues; and calculate a third angle between the reference line and athird tangent line that is tangent to the signature function at a thirdindex value in the set of index values; and a tuple generator togenerate signature values based on the first angle, the second angle,and the third angle.
 12. An apparatus as defined in claim 11, furthercomprising a transducer to convert generate a signal and a sampler togenerate the block of signal samples from the signal.
 13. An apparatusas defined in claim 11, wherein the first tangent line represents afirst linear tangent function, the second tangent line represents asecond linear tangent function.
 14. An apparatus as defined in claim 11,further comprising: a polyphase quadrature filter bank to transform theblock of signal samples to obtain frequency bands; and an energycompactor to perform energy compaction by applying a modified discretecosine transform on the frequency bands to generate the frequency-domainrepresentation.
 15. An apparatus as defined in claim 11, furthercomprising an index selector to: select the first index value; calculatethe second index value based on a first value of the signature functionat the first index value and a derivative of the signature function atthe first index value, the angle calculator to determine the secondtangent line based on the second index value; and calculate the thirdindex value based on a second value of the signature function at thesecond index value and the derivative of the signature function at thesecond index value, the angle calculator to determine the third tangentline based on the third index value.
 16. An apparatus as defined inclaim 11, further comprising a signature generator to generate asignature for media represented by the block of signal samples, by:calculating signature values for additional blocks of signal samplesrepresenting the media; and generating the signature for the media as anordered set of the signature values for the blocks of signal samples.17. An apparatus as defined in claim 16, wherein the tuple generator isto calculate signature values for additional blocks of samples, theblock of signal samples representing the media, and the signaturegenerator is to generate the signature for the media as an ordered setof the signature values.
 18. An apparatus as defined in claim 16,wherein the signature generator is to calculate a mean value of thesignature values, and is to calculate the signature values by bycomparing a mean angle of the first angle, the second angle, and thethird angle to the mean value to determine a signature bit.
 19. Atangible computer readable storage medium comprising computer readableinstructions which, when executed, cause a logic circuit to at least:transform a block of signal samples from a time-domain representation toa frequency-domain representation comprising multiple frequency bands;determine a signature function by fitting a curve to at least a subsetof the frequency bands; and calculate signature values for the block ofsignal samples by: calculating a first angle between a reference lineand a first tangent line that is tangent to the signature function at afirst index value in a set of index values over which the signaturefunction is defined; calculating a second angle between the referenceline and a second tangent line that is tangent to the signature functionat a second index value in the set of index values; calculating a thirdangle between the reference line and a third tangent line that istangent to the signature function at a third index value in the set ofindex values; and create signature values based on the first angle, thesecond angle, and the third angle.
 20. A storage medium as defined inclaim 19, wherein the first tangent line represents a first lineartangent function and the second tangent line represents a second lineartangent function.
 21. A storage medium as defined in claim 19, whereinthe instructions are to cause the logic circuit to fit at least thesubset of the frequency bands by performing least squares error analysisto obtain coefficients for the signature function to fit at least thesubset of the frequency bands.
 22. A storage medium as defined in claim19, wherein the instructions are to cause the logic circuit to createthe signature values by averaging the first angle, the second angle, andthe third angle.
 23. A storage medium as defined in claim 19, whereinthe instructions are further to cause the logic circuit to generate asignature for media represented by the block of signal samples, by:calculating signature values for additional blocks of signal samplesrepresenting the media; and generating the signature for the media as anordered set of the signature values for the blocks of signal samples.24. A storage medium as defined in claim 23, wherein the instructionsare further to cause the logic circuit to transmit the signature to anaudience measurement entity.
 25. A storage medium as defined in claim23, wherein the instructions are to cause the logic circuit to calculatea mean value of the signature values, and instructions are to cause thelogic circuit to calculate the signature values by comparing a meanangle of the first angle, the second angle, and the third angle to themean value to determine a signature bit.
 26. A storage medium as definedin claim 19, wherein the instructions are to cause the logic circuit totransform the block of signal samples by: applying a polyphasequadrature filter bank to the block of signal samples to obtainfrequency bands; and applying a modified discrete cosine transform toperform energy compaction on the frequency bands to generate thefrequency-domain representation.
 27. A storage medium as defined inclaim 19, wherein the instructions are further to cause the logiccircuit to select the subset of the frequency bands in thefrequency-domain representation to include a set of adjacent ones of thefrequency bands that have at least a threshold percentage of a totalenergy in the frequency-domain representation.
 28. A storage medium asdefined in claim 19, wherein the instructions are to cause the logiccircuit to calculate the signature by: selecting the first index value;calculating the second index value based on a first value of thesignature function at the first index value and a derivative of thesignature function at the first index value, the second tangent linebeing determined based on the second index value; and calculating thethird index value based on a second value of the signature function atthe second index value and a derivative of the signature function at thesecond index value, the third tangent line being determined based on thethird index value.
 29. A storage medium as defined in claim 28, whereinthe instructions are to cause the logic circuit to calculate the secondindex value by at least one of rounding or truncating a value at which afirst linear tangent function is equal to a designated value, and theinstructions are to cause the logic circuit to calculate the third indexvalue by at least one of rounding or truncating a value at which asecond linear tangent function is equal to zero. 30-44. (canceled)